Querying value of xml file using xmlstarlet with namspace

using this xml:

<application xmlns="http://ift.tt/VlYZo4">
        <id>5555</id>
        <filename>product2</filename>
        <name>prodigy</name>
        <versionNumber>6.5.511</versionNumber>
        <versionLabel>6.5.5110</versionLabel>
</application>

this command does not work, returns nothing:

xml sel -t -c "/application/versionLabel" application.xml

however, removing the xmlns attribute from application does work. why?